Fixed dimming UIColor's in gray colorspace

Just return this colors as is, they are already grayscale

Before bugfix
![ios simulator screen shot oct 24 2013 11 30 16 am](https://f.cloud.github.com/assets/352555/1397137/d97b9f92-3c7f-11e3-86e0-81e82a14c6d8.png)

After
![ios simulator screen shot oct 24 2013 11 35 51 am](https://f.cloud.github.com/assets/352555/1397138/d997b682-3c7f-11e3-8144-4d173fdf01c4.png)